Semiconductor wafer manufacturing techniques for providing a groove or a specific structure in a semiconductor wafer to accomplish various purposes have been known, as described, e.g., in Japanese Laid-Open Patent Publication Nos. H03-16119, 2002-299761, and 2009-117494. For example, a technique is known for providing a trench in the heteroepitaxial layer on a semiconductor substrate in such a manner that the trench encloses each chip, as described in the above publication No. H03-16119. This trench prevents crystal defects in the epitaxial layer from propagating into the chips even when stress is induced during various manufacturing processes of the semiconductor device. Further, there is known a technique for forming a semiconductor separation layer in a predetermined pattern on the boundary regions between semiconductor chips, as described, e.g., in the above publication No. 2002-299761. This semiconductor separation layer may be used to separate the semiconductor wafer into individual semiconductor chips.
Further, a structure in which grooves are provided in the surface of a semiconductor substrate is known and used to accurately split the wafer, as described, e.g., in the above publication No. 2009-117494.
A semiconductor wafer is manufactured in the following manner: First, InP, InGaAsP, InGaAs, etc. are epitaxially grown on the entire surface of an InP substrate to provide the desired electrical or optical characteristics. Patterns are then formed for each of the identical chips (i.e., minimum product units) to be formed on the substrate. This is accomplished by repeating etching, transferring, and deposition (forming electrically insulating films, electrode films, etc.).
The semiconductor wafer is eventually separated into individual chips each constituting a minimum product unit. On the other hand, there are transactions in which semiconductor wafers with a number of semiconductor devices formed thereon are bought and sold without cutting them into individual chips. Further, some semiconductor wafers are cut into semiconductor bars with a plurality of semiconductor devices thereon, and these bars are traded without cutting them into individual chips. There is a known technique for separating these semiconductor wafers and bars into individual chips. This technique first scribes, e.g., a semiconductor wafer to form a crack therein and then applies external force to the semiconductor wafer so that the crack propagates, resulting in cleavage of the wafer.
If such scribing does not form a suitable crack, that is, if the formed crack does not extend straight perpendicular to the surface of the substrate, then it is not possible to produce suitable cleaved faces (i.e., straight perpendicular cleaved faces at the desired location) in the subsequent chip separation process, which uses the crack as a starting point for cleavage. Failure to form a suitable cleaved face results in production of a chip having an irregular configuration, which chip may be regarded as a defective product or may be difficult to handle in subsequent processes. If the cleaved face is used as a resonator end face of an optical semiconductor device, the quality of the cleaved face is the prime determining factor for the quality of the optical semiconductor device. In view of this, the present inventors have intensively studied cracks formed by scribing, and found the dominant factor in determining their configuration, which factor was not heretofore known.
The object of present invention is to provide a semiconductor wafer and semiconductor bar in which a suitable crack can be formed by scribing, and also to provide a method of manufacturing such a semiconductor wafer, a method of manufacturing such a semiconductor bar, and a method of manufacturing a semiconductor device.
It should be noted that the above dominant factor found by the present inventors is not mentioned in any of the above patent publications Nos. H03-16119, 2002-299761, and 2009-117494, and is a technical fact which was not heretofore known in the art. More specifically, the above three publications do not mention a suitable film structure in which a crack of the desired shape (i.e., a crack extending straight perpendicular to the surface of the substrate) can be formed by scribing its surface.